1. Field of the Invention
The invention relates to magnetic tape cassette recorders with take-up and feed spools for driving tape reels, between which a magnetic tape is moved backward and forward inside the tape-carrying cassette which is placed on the winding spools, and in particular, to adjustable frictional clutches for such recorders.
2. Description of Related Art
Magnetic tape cassette recorders are known in which a capstan motor provided to drive the magnetic tape also drives the winding spools, such as described in DE 3935150, corresponding to U.S. Pat. No. 5,331,481--Schandl and Weisser. A capstan drives the magnetic tape outside of the magnetic tape cassette covering the two winding spools. The capstan motor primarily drives the magnetic tape via the capstan. It also drives the take-up or feed spool selected at the time, these simply being called winding spools in the following, via a drive element, which is a planetary gear system comprising a friction clutch and a tumbler gear, which is non-positively connected to the winding spool which is pulling at the time. Magnetic tape cassette recorders of this type are used as information recording and/or playback equipment, especially in the video and audio field.
The coupling force, which is of a different magnitude for the different operating states, can be adjusted by a clutch ring, which can be moved vertically by a lever, as in U.S. Pat. No. 5,331,481. The contact pressure of the vertically mobile clutch ring against the lower part of the planet carrier, which can rotate about the common stationary shaft, can be adjusted by a motor, e.g. the threading motor, controlling the operating modes, e.g. playback, reverse, search, rewind, via the lever and a cam disc. A compression spring disposed about the stationary shaft presses the planet carrier onto the clutch ring. The planetary gear system can be connected for rewind through projections on the lower planet carrier engaging in recesses in the element, for example a pulley, which is embraced by the drive element, for example a belt, with the assistance of the spring. Because of the coupling between the pulley driven by means the capstan motor and the planet carrier, the ring gear of the planetary gear system and thus the tumbler gear meshing with this gear are directly driven via the planet carrier.
Although this construction has proved successful in practice, because the planetary gear system is connected by using projections and recesses, it requires very accurately produced components and, when using a compression spring to guarantee a constant coupling force, also close component tolerances.